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Physorg.com reports on a recent paper in which the authors analyze the sustainability of algal biodiesel from a mass balance perspective. The paper, Bioresource Tech.102, 1185, essentially highlights one of the tradeoffs with algal biodiesel. The low tech route of large containment ponds limits the total output of dry biomass per hectare, as evidenced by the author’s computation that even 11 square miles of algae ponds, at a growth rate of 50 g of bone-dry biomass per square meter per day, would only be sufficient to replace 0.1% of the US consumption of diesel.

Of course, there are many ways to increase the output per hectare. One of these are vertical tubes, or bioreactors, for algae growth. The issue with this approach is that it is capital intensive, requiring not only the tubes, but cooling systems to prevent algae death from overheating and requires higher overhead, since the tubes must be scrubbed occasionally to reduce fouling.

If I were to be looking at this area for technology breakthroughs, I’d be looking at people applying anti-fouling or other surface chemistry applications to reduce the maintenance costs, or clever engineers designing passive cooling systems for these reactors. I can imagine a system where the bioreactors were built to exchange heat with an HVAC system in cooler environments, or with their own ground-sourced heat pump in warmer times. The cost of the cooling is a major barrier and it would be a win to spread that cost around amongst several different systems.